Exogenous Hematin Alleviates Mercury-induced Oxidative Damage in the Roots of Medicago sativa Effects of Carbon Monox ide on Va se L ife and Antiox ida tive Metabolism inCut Rose Flower Effects of Carbon Monox ide on Va se L ife and Antiox ida tive Metabolism inCut Rose Flower Effect of exogenous carbon monoxide donor Hematin on photosynthesis parameters and chlorophyll fluorescence characteristics of Coptis chinensis seedlings under NaCl stress